Liquid crystal display (LCD) devices generally include an LCD panel and a backlight module under the LCD panel. The backlight module provides a light source to illuminate the LCD panel for displaying images. A cross-sectional view of a conventional direct-type backlight module is shown in FIG. 1. This backlight module 1 includes a plurality of lamps 11, a diffusion plate 12, a reflector 13, a housing 14, and a plurality of optical films 15. The lamps 11 may be cold cathode fluorescent lamps (CCFL) or LED light bars, both of which provide light. The diffusion plate 12 is disposed over the lamps 11 and diffuses the light produced by the lamps 11 onto a liquid crystal panel in a homogeneous manner. The reflector 13 is disposed within the housing 14 and reflects light diffused from the lamps 11 to the inner side of the housing 14 and to the diffusion plate 12. As depicted, the housing 14 is basically a rectangular frame that accommodates the lamps 11, the diffusion plate 12, and the reflector 13. The optical films 15 (such as a brightness-enhancing film and a diffusing film) are disposed on the upper surface of the diffusion plate 12 for adjusting the light emitted from the diffusion plate 12.
A space is maintained between the upper surface of the reflector 13 and the lower surface of the optical films 15 to allow light emitted by the lamps 11 to sufficiently mix. Adequate mixing of light helps to avoid the lamp mura caused by the lamp sources. The height of the light-mixing area is associated with the number of lamps 11 in the module 1. After the number of lamps is determined, the thickness of the light-mixing area, hence the thickness of the conventional backlight module 1, cannot be reduced and still meet the requirement of brightness without producing lamp mura. Thus, the overall thickness of the conventional backlight module 1 is associated with the height of the light-mixing area. Usually, the height of the light-mixing area is more than 20 mm.
Because the required distance between the reflector and optical films prevents reduction of the thickness of conventional direct-type backlight modules, the ability to achieve very slim LCD devices may be limited. Thus, there is a need for thinner and lighter-weight direct-type backlight modules that do not result in appreciable lamp mura and for a liquid crystal display device containing the thinner, lighter-weight direct-type backlight module.